This specification refers to bipolar semiconductor devices, in one or more embodiments to IGBTs and a manufacturing method therefor.
Field-effect controlled switching devices such as Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) or Insulated Gate Bipolar Transistors (IGBTs) have been used for various applications, including use as switches in power supplies and power converters, electric cars, air-conditioners, and even stereo systems. Particularly with regard to power devices capable of switching large currents and/or operating at higher voltages, a low resistance in the conducting on-state is often desired. This means e.g. that, for a given current to be switched, the voltage drop across the switched on IGBT, i.e., the collector-emitter saturation voltage VCEsat, is desired to be low. On the other hand, the losses occurring during switching off or commutating of the IGBT are often also to be kept small to minimize the overall losses. A low VCEsat may be achieved by a high hole plasma concentration in the on-state which in turn tends to increase the switching losses. The trade-off between turn-off performance and VCEsat is, therefore, often unsatisfactory for known IGBTs.
For these and other reasons, there is a need for the present invention.